492 BY-PRODUCTS IN SULPHURIC ACID MANUFACTURE
The cause of this plasticity when grinding might be that
part of the iron oxide was in a colloidal state, and constantly
retained water. Bird found that about 17 per cent moisture
in the purple ore was necessary for briquetting (see infra).
The discovery that roasted ore can be briquetted without any
other binder than water is therefore due to Bird. Grondal and
Dellvik found in 1896 that moistened ore dust from a stamp-
mill could be pressed into briquettes, which after burning became
very solid, showing that iron-ore acted in the same way as
purple ore.
Ram6nl states that the fundamental point of great im-
portance which is often overlooked is the deleterious effect of
the binder used in making the briquettes. The iron content of
the ore being lowered, the cost of production per ton of metal
is increased, whether the binder is of acid or neutral character.
Attention has to be paid not only to the cost of the slagging
of these binders, which is a matter of considerable importance,
but also to the fact that the quantity of iron produced per
unit weight of briquettes is reduced in a corresponding degree.
In contrast with this, the cost of producing pig-iron from a
briquette made without a binder entails a saving of coal, and
gives a greater output, and the commercial aspects of the
smelting operations are improved correspondingly.
In Swedish furnaces using charcoal it has been proved
that by smelting briquettes, which are easily reduced, an
increased output and a considerable saving in fuel have resulted.
With regard to blast-furnaces using coke, an experiment has
recently been made at a German plant In this experiment
2000 tons of purple-ore briquettes from Helsingborg's copper
plant were smelted with coke in a blast-furnace, and the
experience gained by the Swedish furnaces was fully verified.
This test showed a considerable reduction in the coke con-
sumption as well as an increase in the output of pig-iron, also
an increase of 25 to 30 per cent in the capacity of the furnace
The saving in coke amounted to 8 per cent, and would be still
higher in the case of a more regular operation during a longer
period. When figuring the saving which accrues from smelting
briquettes of good quality, as against smelting unbriquetted ore,
1 Lecture given at the meeting of the Verein Deutscher Eisenhutteleute,
ist December 1912.